The present invention relates to an instrumented electrode for providing multivariable data measurements for use in resistance spot welding machines. More specifically this invention concerns an instrumented electrode having a plurality of sensors positioned relative to the electrode end to simultaneously obtain forcing function variables such as welding voltage, current, and mechanical load, as well as response variables such as workpiece surface temperature and displacement due to thermal expansion.
A fairly wide range of instrumentation for resistance spot welding electrodes has been implemented in a variety of prior art approaches, each of which is directed to determining or monitoring primarily only one of the welding parameters considered to be of importance. For example, it is known to provide an instrumented electrode assembly for measuring the voltage drop across a pair of workpieces being joined during resistance welding. In a known arrangement, an insulated wire member is inserted into the interior of an electrode as an electrical attachment to the tip of that electrode for connection to a conventional external voltmeter measuring circuit. Voltage sensing techniques using wires attached to the tips of the pair of electrodes have been used.
The known arrangements are ill suited to meet the ever increasing requirements for higher quality resistance welding devices. No prior art approaches to instrumented welding electrodes have successfully addressed the combination of parameter measurements required to produce a consistently good weld. In particular, with respect to the three groups of welding variables, (1) forcing functions such as voltage, current and mechanical load; (2) response variables such as workpiece surface temperature and electrode displacement due to thermal expansion; and (3) the independent variable time, the prior art is almost totally silent on the need for simultaneously providing the multivariable data required.
The multivariable instrumented spot welding electrode of the present invention addresses these particular needs, and provides a highly advantageous improvement to the art of resistance spot welding sensing and controlling.